Another ship contracted by the Vietnamese state-owned oil and gas group has been disturbed by several foreign boats while it was conducting seismic surveys on the continental shelf of Vietnam, Tuoi Tre reported Wednesday.

The Viking 2, managed by the PetroVietnam Technical Services Corporation (PTSC), was being operated in the waters near Dai Hung oil field, 270 kilometers off the southern province of Vung Tau, according to the newspaper.

According to Tuoi Tre, the Norwegian-flagged ship, which PTSC leased from French-owned CGG Veritas Joint-venture, first encountered a ship at round 9 p.m. on Sunday.

The ship entered the area where the surveys were being conducted, running into Viking 2's tail float, it said.

PSTC's ship then asked for help from two security ships. The other still continued with the disturbance, although it was asked to leave in both English and Vietnamese.

Two survey ships of the Vietnamese oil and gas group PetroVietnam were disturbed by foreign boats while operating on the continental shelf of Vietnam during the past weeks

The troublemaker sped up to the front of Viking 2, prompting the security ships to fire warning flares, Tuoi Tre reported. It only left about two hours later, after Viking No.2 completed its mission.

The newspaper said the security ships couldn't read the ship's name and number, because it used too bright headlights.

The second disturbance was reported to happen between 7:15 a.m. and 8:30 a.m. Tuesday when Viking No.2 was at 8o24'8" N 108o52'5" E.

According to the newspaper, a ship then entered the area, approaching Viking 2 and was some nearly eight nautical miles from PSTC's ship. It was about to cross the ship's tail float before a security ship stopped it.

Another ship, which was also nearly eight nautical miles from Viking 2, meanwhile, approached it from behind, but was stopped by the security ship as well.

The security ship found one of the two ships causing problems was named Fei Sheng No.16, while the other carried the number BI2549, Tuoi Tre reported, adding that both the ships didn't respond to Viking 2's efforts to communicate with them.

It said PTSC has reported the case to PetroVietnam, while Viking 2 is still operating as normal. It is currently engaged in seismic surveys under a contract between PetroVietnam and Japanese-owned IDEMITSU.

Nguyen Hung Dung, director general of PTSC, told the newspaper that over the past few days a ship conducting seismic surveys in the area of southern Vietnam's continental shelf has been disturbed in recent days.

But, he didn't say which the troubled ship is.

Last Thursday, the Binh Minh 02, a ship of PetroVietnam, had its cables cut by Chinese patrol ships when it was conducting oil exploration. The incident happened when the ship was in Vietnam's territorial waters, some 120 nautical miles off the central coast.